A new pushdown automata based algorithm for searching all occurrences of a tree pattern in a subject tree is presented. The algorithm allows pattern matching with don’t care symbols and multiple patterns. A simulation algorithm is also proposed, and practical experimental results are presented.

We show that several basic discounted properties of probabilistic pushdown automata related both to terminating and non-terminating runs can be efficiently approximated up to an arbitrarily small given precision.

We analyze models of infinite-state automata extended by monotonic counting mechanisms, starting from the (finite-state) Parikh automata studied by Klaedtke and Rueß. We show that, for linearbounded automata, this extension does not increase the language recognition power. In the framework of infinite transition systems developed by Caucal and others, we show that adding monotonic counters to s...

We show that several basic discounted properties of probabilistic pushdown automata related both to terminating and non-terminating runs can be efficiently approximated up to an arbitrarily small given precision.

Recently, we showed that first-order model checking on nested pushdown trees can be done in doubly exponential alternating time with linear many alternations. Using the interpretation method of Compton and Henson we give a matching lower bound.

We give a new proof of the decidability of reachability in alternating pushdown systems, showing that it is a simple consequence of a cut-elimination theorem for some natural-deduction style inference systems. Then, we show how this result can be used to extend an alternating pushdown system into a complete system where for every configuration A, either A or ¬A is provable.

It is well-known that an effective orbifold M (one for which the local stabilizer groups act effectively) can be presented as a quotient of a smooth manifold P by a locally free action of a compact lie group K. We use the language of groupoids to provide a partial answer to the question of whether a noneffective orbifold can be so presented. We also note some connections to stacks and gerbes.

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We use a relational characterization of binary direct sums to model sequences within the relation-algebraic manipulation and prototyping system RelView in a simple way. As an application we formally derive a RelView program for computing equivalence classes of an equivalence relation, where we combine relation-algebraic calculations with the so-called Dijkstra-Gries program development method. ...